Five years and $1.8m in the making, the John Jay College report on the "causes and context" of the sexual abuse crisis in American Catholicism that was released last week has an excellent story to tell.

The report identifies the crisis as a mountain of incidents, rising steadily from sea level in 1950 to a peak in 1980, then declining precipitously to a permanent low plateau in the mid-1990s.

It divides the relevant priests into "cohorts" according to decade of ordination, and asserts that in each case, "the participation in sexual abuse of the cohort rises in the 1960s and 1970s and falls in the 1980s".

So the decades made them do it: "The period of elevated incidence and subsequent decline are thus seen as period effects that were shaped by general social factors." The 1960s and 1970s encouraged bad behaviour of all sorts, but in the 1980s there was "a reduced tolerance for behavioural deviance in society in general".

The only problem with the story is that the actual statistics don't support it.

According to the report's own graphs, abuse by the pre-1960 cohort rises in the 1950s, remains constant in the 1960s, and begins to decline in the 1970s. For the 1960s cohort, abuse rises in the 1960s, remains constant in the 1970s, and declines in the 1980s.

"The 60s" cannot account for increased abuse in the 50s. And if the 60s and 70s were so morally permissive, why did abuse among these two cohorts level off and/or fall?

In fact, according to the graphs, the entire increase in abuse cases during the 60s and 80s comes about as a result of abuse on the part of the cohort ordained in that decade – which is to say that as more priests joined the cohort, more priests in the cohort abused. Duh!

The actual explanation for the statistics would seem to have to do more with the demographics of the American priesthood and the vagaries of reporting than with changes in the culture. Over 90% of the abuse cases were reported in the past decade, after the Boston Globe did its celebrated investigative series on the handling of abusing priests in the Boston archdiocese. Given the age of the victims when the reports were made, it is hardly a surprise that there should be very few cases dating back to the early 50s.

Moving forward, the number of cases tracks the priesthood boom of the postwar period and the post-60s bust, during which the population of active priests shrank and aged.

This is not to say that "the 60s" had no effect whatsoever. Anecdotally, one can point to examples of priests who acted out the sexual liberation of the era in criminal ways. Similarly, the decline in the number of cases in the 1980s and 1990s can plausibly be related to a new societal recognition of the dangers and extent of child sexual abuse, and the states' enhanced criminal laws punishing it. But the evidence for a disproportionately large, culturally induced outbreak of child abuse by Catholic priests of all ages in the 1960s and 1970s simply isn't there.

What the Woodstock defence does, however, is direct attention away from the real abuse crisis: the failure of bishop after bishop to deal properly with their abusing priests once American society at large had begun to take the problem seriously. Nor did the bishops lack for opportunities to do the right thing.

In 1985, after the first nationally notorious priest abuse case, they declined to adopt an action plan that would have created a uniform approach to dealing with the problem. In 1992, after a second major national scandal, they adopted a set of five principles – among them, complying with civil law in reporting incidents – as the recommended course of action. But the principles were widely ignored.

Not until 2002 did the bishops, under pressure of the greatest crisis in the history of American Catholicism, adopt norms mandating serious steps to deal with abuse cases, including a zero tolerance policy for priests credibly charged with offenses. But as a Philadelphia grand jury's report made clear this year, even then there would be bishops who continued to keep abusers on the job.

To its credit, the report does not hesitate to speak of the "failures of institutional response". But an adequate "causes and context" report would have spent less time trying to calibrate the situation of the abusing priests and more time assessing the culture of the diocesan authorities who protected and enabled them.

It would have weighed the importance of a celibate, all-male clergy in a clericalist culture that considered its first duty to be to look after its own. It would have scrutinised the canon law doctrine of scandal and how this was continually used to justify the failure to report criminal acts. And it would have explored the lines of connection to cops and judges, to politicians and psychologists, that began to fray in the 1980s.

The true brilliance of the Woodstock defence is that by pretending that child sexual abuse was a "period effect" of "elevated incidence", it can dismiss celibacy and an all-male priesthood as ecclesiastical constants incapable of being causal factors. It can ignore the fact that what created the crisis was not some new acquiescence in behavioural deviance but an enhanced standard of criminal accountability that rendered unacceptable the old diocesan ways of doing business.

It was the bishops, however, who commissioned the report, who set its terms, and who controlled and continue to control access to the files. It was the bishops who were the clients and, in the end, they got the report they paid for.